Camshaft grinding machine



Feb. 1, 1949. c. J. GREEN CAMSHAFT GRINDING MACHINE Filed June e, 1947 4 Sheets-Sheet 1 Fa. y 1

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I Invenroz Cinemas a]. Gees/v H rrozHE: Y

Feb. 1, 1949. c. J. GREEN 2,460,744

CAMSHAI'T GRINDING MACHINE Filed June 6, 1947 4 Sheets-Sheet 2 lNvzHroa CLARENCE d. G255 B Museum Feb. 1,1949. I QIGREEN 2,460,744

CAMSHAFT GRINDING MACHINE Filed June 6, 1947 4 Shets-Sheet 3 4 INVEHTOR Cunzanca d. Gaza/1 BYMLO-W F? TTOIZNEY Patented Feb. 1, 1949 CAMSHAFT GRINDING MACHINE Clarence J. Green, Worcester, Mass, assignor to Norton Company, Worcester, Mass, a corporation of Massachusetts Application June 6, 1947, Serial No. 752,978

5 Claims.

The invention relates to grinding machines, and more particularly to a camshaft grinding machine.

One object of the invention is to provide a simple and thoroughly practical camshaft grinding machine. is to provide a camshaft grinding machine which is arranged to grind all of the cams and main bearings on a camshaft. Another object is to provide an automatically actuated mechanism to control the duration of the cam and bearing grinding operations. vide an electric counter mechanism to control the duration of the cam grinding operation, and

an electric timer to control the duration of the bearing grinding operation.

A further object is to provide an automatic control for the electric counter and timer which is arranged so that when the grinding wheel feed is initiated, the counter or timer are rendered operative depending upon whether a cam or a bearing is positioned for a grinding operation.

Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements,-

and arrangements of parts, as will be exemplified in the structure to be hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which is shown one of various possible embodiments of the mechanical features of this invention:

Fig. 1 is a front elevation of the improved camshaft grinding machine;

Fig. 2 is a cross sectional view, on an enlarged scale, through the machine, taken approximately on the line 2-2 of Fig. 1, showing the work head and the wheel head in elevation;

Fig. 3 is a combined hydraulic and electrical diagram of the wheel feeding mechanism and the controls therefor;

Fig. 4 is a longitudinal sectional view, on an enlarged scale, through the solenoid actuated feed control valve;

Fig. 5 is a diagrammatic perspective view showing the operative relationship of the various mechanisms;

Fig. 6 is a fragmentary rear view, showing the master cam roller indexing mechanism;

Fig. 7 is a fragmentary view, on an enlarged scale, of the star wheel and dog bar and other associated parts of the master cam roller indexing mechanism;

Fig. 8 is an electric wiring diagram of the Another object of the invention Another object is to pro-H.

electrical controls for the wheel feeding mechanism; and

Fig. 9 is a fragmentary sectional view, on an enlarged scale, of a modified construction for use in positioning the rock bar for a bearing grinding operation.

A camshaft grindingmachine has been illustrated in the drawings having a base I which supports a longitudinally movable work table II on the usual fiat way l2 and V -Way I3. The base I 0 also supports a transversely movable wheel slide l which is mounted on the usual fiat way l6 and V-way I! for a transverse adjustment toward and from the work supporting table II. The wheel slide l5 rotatably supports a grinding wheel spindle 18 in suitable bearings (not shown); The wheel'spindle I8 carries a grinding wheel l9 which is arranged to present a peripheral cylindrical grinding face to the work piece for a grinding operation. The grinding wheel I9 and its supporting spindle l8 may be driven by means of an electric motor 20 mounted on the upper surface of the wheel slide IS. A pulley 2| is mounted on the motor shaft and is connected by a driving belt 22 with a pulley 23 mounted on the wheel spindle i8.

The work table H serves as a support for a rock bar 25 which is supported on trunnion studs 26 and 21 (Fig. 5). The trunnion studs 26 and 21 are supported in bearings (not shown) which are fixedly mounted on the table II. The rock bar 25 is provided with a head stock center 28 and a foot stock center 29 rotatably to support a camshaft 30. The camshaft 30 is provided with a plurality of integral cams 3| and bearings 32 to be ground.

In order to generate predetermined contours on the cams 3!, a master camshaft 33 is rotatably su-pported on the rock bar 25 in axial alignment with the centers 28 and 29. The shaft 33 serves as a. support for a plurality of master cams 34 and a plurality of master bearings 35. A rotatable master cam roller 36 is slidably mounted on a rotatable shaft 31 which is rotatably supported in bearings fixed relative to the table II. a

The master cam roller 36 is arranged so that it may be'indexed longitudinally in timed relationship with the indexing movement of the table II so that when the table II is indexed longitudinally to position a .cam' 3| or a bearing 32 opposite the grinding wheel IS, the master cam roller will be automatically indexed to a Position opposite the master cam 34 or the master bearing 35 corresponding to the cam or'bearing to be ground.

A suitable mechanism is provided yieldably to maintain the master cams 34 and the master bearings 35 in engagement with the master cam roller 36 during a grinding operation and to separate the master cams and bearings from the roller during'atable-indexing movement; The rock bar 25 islprovidediwithaan arm 46 which is'con nected to the end of a piston rod 4!. A piston 42 is mounted on the upper end of the piston rod;

M and is slidably supported withina cylinder 43.

A compression spring 44 surrounds the piston rod 4i and is interposed between thepiston 42 1andan end cap at thelower end.of' the" cylinder43 The compression spring 44 normally serves to maintain the master teams 34 orthe master bearv ings 35 yieldably in engagement with the master cam roller 36 during a grinding operation; When it is desired to index the table H longitudinally to: position anew cam. 34 or bearing 32 in opera? tive relationship with the grinding wheel: 19,. fluidl under. pressure: is. admitted through. a: pipe 45 intoh= a cylinder chamber 46=to cause a downgwardgmovementofi the piston 62 whichser-vesto rock the rock bar 25 in a counterclockwiserdirec tiony. (Figsl. 3-;and-5): to. separate the master cams andbearings from: the:master:cam roller: 36; dur:-- ing; a table indexing-movement.

The table: I I may: be traversedl longitudinallyby-a manually operable traversemeclranism comprising-a hand wheel56 which" isoperatively con:-

Y 'nected to a traim ofagears (not; shown) with a rackibarifi depending from the.undersid'e ofthe a table ll: (Fig; 2),; 'This mechanism' is substantially identical. with that: shown: in r the prior. United.- Statess. Patent No; 1,783,755 to.- C.. G: 'Irefethen; etqaL, dated December: 2, 1930,110 which reference maybeih'a'dxfor; details of dis-- closure notxcontaine'd hereinz.

.An automaticallyoperated. indexing meehanism: is provided for indexing the master cam roller. ,36- longitudinally inzti'm'ed relationship with the: indexingmovement: of: the .work table I sothat when -the' table; is :indexed: to position acamadjustable dogs. 56: which are arranged in: the

path of a star wheel 51. Thetstar. wheelis V V mounted onarotatableshaft: 58 which carries a gear 59ameshing1with a gear 66 on the stud 6!; The; gear-66 meshes with a-gear'BZJcarriedbya shaft or stud 63...- The shaft 63 also supportsaa gear 764 which? meshes with the rack bar 5.3a. It

" will be readily apparentirom the-foregoing dise closure that when the table. It ismoveddongie t'udinally a corresponding, movement is. imparted to the star wheeland. the. gear trainaboveldescribed. When the star Wheel moves intoiengagement with oneof the dogs Won the dog'bar 51'; a rotary motion is transmitted to thefgear train to transmit a longitudinal indexing movement tothe' rack bar; th'e'yoke' 2: to index' th'e master cam roller 36'longitudina'lly; The dogs'55 are adjustablypositioned on' the dog bar 5t to correspond with the spacingof the" cams 3F'on the sh'aft' 30 so that whenthe'tableis indexed to po'sition any one of the ca-ms-iil' era; grinding operation, the master cam roller 36 will be indexed into operative with the corresponding master cam 34.

In order to control the grinding cycle while grinding a bearing 32 on the camshaft 36, a roller 65 is mounted on the left hand end of the shaft 58 (Fig. '7). The roller 65 is arranged in the path of; aplurality of limit switches 66, 621? and 6B which are supported on a bar d9 whiclris=' fixedly mounted on a bracket 55. When the table H is indexed longitudinally to position one of the bearings 32 for: a grinding operation, the roller 65 will enga'g e the corresponding'limlt switch so as to' 'render an electrical control mechanism to be hereinafter described operative to control the grinding feed'on the bearin to be ground. The limitswitches 66, 6-1, and 66 are spaced on the bar 69 to correspond with the spacing of the bearings 32'' onth'e camshaft 36 to be ground. There is one limit switch for each bearing on the camshaft-'. lnz'the present case there are three bearings: to be ground and; consequently there are three limit switches 66, 61, and 68. Iiiaishaft to be: ground has more. than. threebearirrgs to round, then: additional limit;sw-itc"hes areipinvidedion the:bar:'69:.

V A suitable wheell feedingmechanism? is preevided for controlling the feeding movement oi the grinding wheel:- durin the grinding or cams 31 andbe'arings iizi on the: camshaft 36.1. This feeding: mechanism: comprises a' mta'table feed" screw-l5+ (Ei'gs.-2 and 3.) which meshes withor: engages a half 'nutllfi: depending from the und'er side ot'the wheel'-slide;"l5; A manually" operablefeed wheelfli (Figs. Land 2) is: provided for manually rotating the:feed:serewwe to: impart a transverse movemenntwthe wheel) slide 15:.

In-orderx tovv move the" wheel slide rapidly to and? from a grinding. position and toraut'omatically' control the 1 feed: thereof during grinding, a hydraulically operated: mechanism is provided comprising a: cylinder? 7.8 which relative to thebase In; Theicylinder'lllicontainsalslid ably mounted piston 19 whiclrisconne'cted to=a doublei endi pistonv rod 86;: The. left lriandend of thepiston rodth 'isconnectediby means ofia cowplihg. '81 witltrztheiright end. of th'e .-fee'd' screw 15;. The coupling. 8.1 is arranged so that thefeed screw' 15.. may? be Jotatedf without imparting arotary motion to thepiston rod'86.-

A feed control valve 82: is provided for con trolling the: admission to and exhaust-of fluid from the'cylinder T8. The valve trims-preferably a=piston type valve'comprisihg avalve stem 83 having formed integral tlierewith "'v-al ve pistons 843.65,- 86 anditll A compre'ssionspring-SE serves normally: to .maintain the valvestem 83 hr its right hand end posi tionas i'llustrated Fig. 4'. A push-type solenoid 89" is providedto shift the valve stem--8'3- toward" the left when it is: desired to initiate a" forward feeding movement of the grinding wheel 19. Fluid under-"pressure from a pump (not shown-Y is'passed throu ghapipe-eii into a-va-lve' chamber fi'l located between the valve pistons and 86. In the positionof the valve 3-2 (Fig. 4") fluid underpressure entering the -va-lve chamber '91 passes through a pipe 92' into a cylinder chamber 93 to cause the piston 19* together wan the feed screw}'L'i an'd wheel slide l 5 to move toward the-right (Fig; 3) to move thegrin-ding wheel It! to a rearward or inoperative position. During this" movement; fluid within a cylinder chamber 94 may" exhaust through a pipe 95 into a valve chamber 96 located between the valve pistons 84an'd 85 and" pass out through a"- port 5 91, a passage 98, and a pipe 99 into the reservoir contained within the base of the machine;

When the solenoid 89 is energized to shift the valve stem 83 into its left hand end position, fluid under pressure passing from the pipe 99 into the valve chamber SI passes out through the pipe 85 into the cylinderchamber St to cause the piston 19 to move toward the left (Fig. 3) to move the grinding wheel I9 rapidly toward the work piece to be ground. During this movement of the grinding wheel I9, fluid within the cylinder chamber 93 may exhaust through the pipe 92, through a valve chamber I located between the valve pistons 85 and 8'! and pass out through a port IUI, through the passage 98 and the exhaust pipe 99 into the reservoir.

In order to slow down the rapid approaching movement of the grinding wheel 59, a dash pot feed regulator is provided comprising a pair of diametrically opposed dash pot pistons I66 and I07. A rearwardly extending portion of the piston rod 86 is provided with an adjustable nut I08 which is arranged to engage the right hand end of a collar I99. The rapid approaching movement of the wheel continues until the nut I88 engages the collar I69 and starts movement of the dash pot pistons I86 and Illl' toward the left (Fig. 3). Fluid from the dash pot cylinders is exhausted through a pipe Iii and a needle valve ili into a reservoir I I2. A pipe H6 is also connected to the left hand end of both of the dash pot cylinders to control the exhaust of fluid through a second needle valve In and a pipe II8 into the reservoir H2. During the initial movement of the dash pot pistons I06 and IIl'I toward the left, the exhaust of fluid from both of the dash pot cylinders is controlled by the setting of needle valves HI and Ill! to produce a shoulder grinding or a rough grinding feed. After the dash pot pistons close the port at the end of the pipe I Hi, the exhaust of fluid is thereafter controlled by valve II? which is set to produce a slower or finish grinding feed.

In order to maintain sufficient fluid within the reservoir I I2, fluid under pressure from the pump (not shown) is conveyed through a pipe i I3, and a relief valve II-t which is set to pass a relatively low pressure fluid through the relief valve II l. Excess fluid under pressure entering the relief valve H4 is returned through a pipe II into the reservoir. A pipe i26 connects the relief valve H4 with the reservoir H2. A control valve I2I is provided in the pipe line I28. Compression springs are provided within the dashpot cylinders to return the dashpot pistons I86 and ID! toward the right into an inoperative position when the wheel slide it and grinding wheel I9 are moved rearwardly to inoperative positions, In order to facilitate-the passage. of fluid through pipe lie to fill the dash pot cylinder chambers, a check valve H9 is provided which opens to allow rapid passage of fluid to bypass around the needle valve ill, rapidly to fill the dash pot cylinder chambers.

A modified construction has been illustrated in Fig. 9 for controlling and positioning the rock bar during a bearing grinding operation. As shown and described above cylindrically shaped master bearings have been provided for locating the rock bar relative to the master cam follower roller during a bearing grinding operation. During the bearing grinding operation there is no rocking movement of the bar 25 but it is merely necessary to position the bar in a fixed position and to maintain it in this position'during the grinding of the bearings 32 on the'camshaft 30.- As illustrated in Fig. 9, the rock bar 25 may be provided with a plurality of brackets I46 which are fixedly mounted on the upper surface of the rock bar 25 and spaced thereon to correspond with the main bearings 32 on the camshaft 30 to be ground. An adjusting screw MI is mounted on the upper end of the bracket I40. The adjusting screw Mi is provided with an enlarged head I42. having a plane surface which is arranged to engage the periphery of the master cam roller 36 to position the rock bar 25 during a bearing grinding operation. It will be readily apparent from the foregoingdisclosure that the adjusting screw IM may be adjusted precisely to adjust the position of the rock bar 25 relative to the master cam roller 36 in'setting up the machine for a grinding operation.

A work driving motor 38 is mounted on a work head casing 33 (Fig. l) which is operatively connected to rotate the master camshaft 33 and the camshaft 30 to be ground. The driving connections between the motor 38 and the master camshaft 33 are identical with that shown in the prior United States Patent No. 2,194,434 to Herbert A. Silven dated March 19, 1940, to which reference may be had for details of disclosure not contained herein.

An electrical control apparatus is provided including a source of power, as indicated by a pair of power lines LI and L2 (Figs. 3 and 8). A control lever I26 is pivotally supported on a stud I21 on the front of the base Ill. When the lever I 26 is moved in a counterclockwise direction (Fig. 3), a cycle start switch is closed to start a grinding cycle by energizing the solenoid 89. If it is direction (Fig. 3) to open a cycle stop switch I29.

The closing of the cycle start switch I28 serves through a pair of control relays CR! and CR2 to energize the solenoid 89 so as to shift the control valve 82 to initiate an infeeding movement of the grinding wheel IS. The control relays CRI' and CR2 serve to render either an electric timer I36 or an electric counter I3I operative to control the duration of a bearing or a cam grinding cycle respectively. A normally closed limit switch LSI (Figs. 3 and 8) is actuated by an adjustable screw I32 carried by an arm I33 on the rock bar 25. Each time the rock bar is rocked during a cam grinding operation, that is, once during each rotation of the master camshaft and the camshaft being ground, the switch LSI is opened to impart an impulse to the counter I3I. After a predetermined number of rotations of the camshaft 36 being ground, that is, after a predetermined number of impulses of the counter I3I, the solenoid 89 is deenergized thereby releasing the compression of the spring 88 which shifts the control valve 82 into a reverse position to move the grinding wheel I9 rearwardly into an inoperative position and thereby to terminate a cam grinding operation.

When the table II is indexed to position one of the bearings 32 for a grinding operation, the roller 65 is moved to actuate and open one of the limit switches (LS2-Fig. 8) 66, 61, or 68 (Fig. 6).-

Opening of one of the limit switches serves to render the timer I30 operative to control the grinding cycle so that the solenoid 89 remains energized for a predetermined time interval.

After a predetermined time interval has elapsed,

. trol': a cam: grinding cycle.v

area-24st released compression oil the springf w to shift the accompanying drawingsris to: be mtei'preted as;

illustrative not in a;- limiting. sense valve 82' into reverse-position to move the grinding Wheel I 9 rearwardly' to an. inoperative position; and thereby to ternnnate a; bearinggrinding operation.

j While the limit sWit'ches (-LS-2-Fi'g a) 66 61 and: 6% remain closed; the timer is renderelsl in operative and the counter- 13-1 operative to co'H- E H Operation justments to have previously been made; a; shaft 30;having;a plurality of cams 3 t and'bear ings- 32 to be ground is mounted- 011 08111781 5 28 ing: motor and the work driving motor 38 are: started. The j manually operable traverse wheeL 50risv-rotated to index the table I I so asto positioneitheracanr 30 or a'bea-ring 32- to be gro'un'drin anoperative positionvopposit'e the g-rinding'wheel l9. During the table indexing; movement, the? master cam: roller 36/ is automatically indexed:

into operative relation with the master cam 34- V ormaster bearing- 35 corresponding: to the cam V 31 or bearing 32: to=be ground. The control lever- I 26- is then rocked inla' counterclockwise f direction (Fig.3) to close the cycle start switch I281 C1os-* ing, switchl28 servesto energize'the solenoid 8'9 toshift valve'stem 83 into an extremeileft 1 position toinitiate-a rapid-approaching movement? until the nut H38 engages the sleeve [09 after which the'dash'pot pistons l flfi'and Hi7 slow down the rapid approaching toa slow grinding. ieedi Atithe same'" time: the cycle start; switch". me is:

closed, either the electric timer- L30 orthe'electrio counter I31 is rendered roperative dependingI'upon whethera bearing'32 or a cam 31' is tol'be'groundi The: grinding operation continues for either" apredetermined time interval: or a predetermined number of impulses of thecounter? after. which the sole'noid 89 is deenergized to releaseit h'e com pression of the spring '88 which shifts the valve 82'; into a; reverse position rapidly to move'thei In" a camshaft grinding: machine haying a; transverselymovable: rotatable grinding? wheel; a longitudinally movable table; a rock-bar on: said table;- a master: camshaft retatabl y' supported on said rock: bar; a pineal-it ofspaced master aiii'cl master beai ilig s' on said: shaft} a hads'tool and aifoot'stock center on" said rocl't liar in axiail allig'i'iinefnt 'vvith" th mastr camshaft rdfaitably to su'pport a; camshafthaving apliil alifiy (if-spaced cams and bearings j to 'bei'g l oufid a sli'daiol'y' mounted rotatable: mastercam roller on said table; an electric counter actiiated 15y oscillation of the rock bar which is'rendered: operative when acam is ii i-a-n' operative grinding position to controi the duration of a cam grinding operation, and el'ectric timer which is rendered operative and. Therotatmn of the'grinding wheel=drivwhen a bearmg m an (lemme gnndmg DO 1 tion to controi' the duration of a bearing" grinding operation. 7

21in" a' camshaft grinding machine having" a transversely movable-rotatablegrinding wheel, alongitudinally movablet'abl'e', means'includifig aliyd'i'aulic' piston and cylinder tomove' said wheel transversely in either direction, a solenoid ac}: tuatedcontrol valve-therefor, arock bar on said table; a" master camshaft rotatably" to rock said baija plurality of spaced mastercams'andma ter hearingson said shaft, a' headstock and a' foot stock center on said rock bar in axial alignment with the master can'i'shait' rotatably to support a camshaft having a' plurai'ity-ofspaced cams and bearings tobeground, atable-indeXed slid== a-b'lymounted master' cam' r'ol'l'e'r on said ,table; an electric counter actuated by oscillation of the rock' b'ar whichdsrendered operative-When a camisin an operative: grinding position'to actuate" said soleiio'idvalvetb'cause'aj reaiiwardjmovement of the grinding wheel 15'0"" an inoperative position after a predetermined cam gi inding o'peration; and an electric tuner which isrendered operative whena" bearing is in an operative grinding position-to" actuate said sol'eiioidi Valve to cause a rearward movement of' the g'iinding wheerto an inoperative position after a redeter'mined teargrinding Wheel: l9 to'a rearwardi or inoperative position. The table H may/then beindexedato position the next cam 3| or bearing? 32: mm a grindin osition after which the: grinding cycle is repeated until all of the-cams; 31 andzbearings 32llhave been ground:

- As illustrated in the drawing: an described;v above: the table H- is indexed manually: by? rota tion ofithehanditrav'ersewheel I f desired the table I may be indexed automatlcally in a' ni'an' n'er similar to that disclosed in the prior United Statesi'p'a't'ent to Herbert A. Silven; No; 22194343 1 dated'March' 19, 1940, to whicli reference ma be" had for details of di'sclosuremot c'ontained herein;

will thus-be seen-that there-lias been=prov idd by this invention apparatus in which the various object's hereinabojve set forth to'gether in grinding-operation" lias -ibeen 'completed';

Ina' -ca-mshaft grinding machine having a transversely movable rotatablegrinding wheel} alongitudinally movabletable, means including a piston and cylinder to move" saidw-heeltrans verselyin either direction, a solenoidactuated initiate a forwardfedi-iigmovement (if the gri'rid ing'wheel; a rockba-r on said table; a master'camshaftrota-tably supported on said rock bar, a pliirality of-spacedmaster cams' and ma'st'er b'ear': in'g's on said shaft; a headstbok and a footst'ock center-on said foclharin axial aligmnent w-itli the: master" cam rotatably to support acamshafthavin'gaa; pluralityof? spaced cams and hearings to be ground, a slidably mounted'mtatable master cam: follower on said table, an electric counter actuatedby oscillation f the rock bar" which isrendered operative when a cam is inan' operative grinding. position tov actuate saidsolenoid valve after atpredeter-min'ed cam grindingoperation to cause-a rearwardfmovement oft lie grindingvwheel to an' inoperative position so as to control the duration of a cam" grinding o eration, and an electric timer" which is rendered operative when a-bearing is'iiran operativegriiidmg osition to movement of the grinding wheel to an inoperative position after a predetermined bearing grinding operation so-as to control the duration of the bearing grinding operation.

4. In a camshaft grinding machine having a t1-ansverselymovable rotatable grinding wheel, a longitudinally movable table, a rock bar on said table, a master camshaft rotatably supported on said rook bar, a plurality of spaced master cams and bearings on said shaft, a headstock and a footstock center on said rock bar in axial alignment with the master camshaft rotatably to support a camshaft having a plurality of spaced cams and hearings to be ground, a table-indexed slidably mounted master cam roller, an electric counter, a limit switch actuated by oscillation of said rock bar to actuate said counter to control the duration of a cam grinding operation, a plurality of limit switches, one of said limit switches being arranged to be actuated when the camshaft is moved longitudinally to position a bearing for grinding, and an electric timer rendered operative by said switches to control the duration of the bearing grinding operation.

5. In a cam grinding machine having a transversely movable rotatable grinding wheel, a longitudinally movable table, a rock bar on said table, a master camshaft rotatably supported on said rock bar, a plurality of spaced master cams on 10 said shaft, a headstock and a footstock center on said rock bar to support a camshaft having a plurality of spaced cams and bearings to be ground, a rotatable slidably mounted master cam roller on said table, means including a dog bar having a plurality of adjustable dogs and a star wheel to index the master cam roller in timed relation with the table indexing movement, a plurality of spaced adjustably mounted screws on said rock bar located between said master cams which'are spaced to correspond with spaced bearings on the camshaft to be ground, said screws being arranged to engage said roller when a main bearing is in a grinding position, a plurality of spaced limit switches actuated in timed relation with said star wheel, and an electric timer rendered operative by said limit switches to control the duration of a bearing grinding operation.

CLARENCE J. GREEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,251,882 Green Aug. 5, 1941 2,284,606 Flygare et al May 26, 1942 

